This invention relates to a cooling system for internal combustion engines, and more particularly to an improvement in the cooling device for an engine coolant flowing through the engine.
In connection with engine cooling systems of motor vehicle engines wherein an engine coolant is cooled by a radiator, it is well known that a cooling fan for the engine coolant is directly connected to a rotatable spindle of a water pump which is driven by an engine crank shaft. This type of the cooling system has encountered the following problems: since engine output power consumed for driving the cooling fan increases approximately proportionally to the cube of the rotational speed of the cooling fan, a considerably large amount of the engine output power is consumed during engine acceleration under high engine speed operation and accordingly acceleration performance of the engine in such an acceleration is deteriorated with degraded engine output power and degraded fuel consumption. Furthermore, noise generated by the rotating cooling fan abruptly increases during the high speed operation in addition to increased engine noise.
In this connection, it is experienced that the consumed engine output power and the noises from the cooling fan considerably increase during engine acceleration under urban area cruising in which a throttle valve is fully opened, for example, under an operating condition where engine speed is higher than 4000 rpm, the gear in a gear box is in first or second gear position, and vehicle speed is about 50 km/h. It will be understood that such an operating condition does not continue for a long period of time and perhaps continues for 60 seconds at the most. Therefore, stopping the driven rotation of the cooling fan does not invite any trouble under such an operating condition. Conversely, such an engine operating condition continues for a long period of time during long uphill crusing a mountainous area or a suburban area, and accordingly engine overheating is liable to occur. Therefore, high speed driven rotation of the cooling fan must be maintained in this long uphill cruising of the vehicle.